Two-dimensional x-ray diffraction refers to x-ray diffraction applications with a two-dimensional diffraction image and corresponding data reduction and analysis. A two-dimensional diffraction pattern contains far more information than a one-dimensional profile collected with a conventional diffractometer. In recent years, usage of two-dimensional (2D) detectors has dramatically increased due to advances in detector technology, point beam x-ray optics, and computing power. A two-dimensional diffractometer is a diffraction system with the capability of acquiring a diffraction pattern in two-dimensional space and analyzing 2D diffraction data accordingly. A typical two-dimensional diffractometer system 10 normally consists of five major units as shown in FIG. 1. An X-ray generator 12 produces x-rays with the required radiation energy, focal spot size and intensity. X-ray optics 14 condition the primary x-ray beam to the required wavelength, beam focus size, beam profile and divergence. A goniometer and sample stage 16 establish and maneuver the geometric relationship between primary beam, sample and detector. A sample alignment and monitoring system 18 assists users in positioning the sample at the instrument center and monitoring the sample state and position. And a two-dimensional detector 20 intercepts and records the x-rays scattered from a sample and, along with a processing unit, saves and displays the diffraction pattern into a two-dimensional image frame.
Another method of collecting diffraction data uses a point detector that is scanned around the sample along a detection circle. FIG. 2 is a schematic view of a method of x-ray diffraction from a powder (polycrystalline) sample. The figure shows graphically a conical distribution of diffracted x-ray energy. For simplicity, the figure shows only two diffraction cones, one representing forward diffraction (2θ<90°) and one representing backward diffraction (2θ>90°). In actuality, the diffraction pattern from the polycrystalline sample forms a series of diffraction cones, assuming a large number of crystals are oriented randomly in the space are covered by the incident x-ray beam. Each diffraction cone corresponds to the diffraction from the same family of crystalline planes in all the participating grains.
The diffraction measurement in a conventional diffractometer is confined within a plane, here referred to as the diffractometer plane 22. In FIG. 2, a point detector 24 makes a 2θ scan along a detection circle 26 located within the diffractometer plane. At points all along the circle, the detector 24 detects the diffracted x-rays. This information is assembled to provide an indication of the diffraction pattern along the detection circle. Thus, the diffraction profile covers only the diffraction intensity variation within the diffractometer plane. Since the diffraction data out of the diffractometer plane is not detected, this additional information is either ignored, or is measured by various additional scans with the sample in different orientations.